An interactive still frame television distribution system is disclosed, for example, in U.S. Pat. No. 4,734,764. Such a system is particularly suited for interactive video services such as home shopping, financial transactions, education and the like. Generally speaking, in this type of system a viewer sends an indication to a central location describing a video presentation which he desires to receive, e.g. houses being offered for sale by a real estate service. Video frames which show the available houses are individually retrieved from a suitable video storage medium, and each frame is labelled with an identification code which enables it to be retrieved by the viewer who desires to see it. Other viewers can independently request other presentations available on the system. All of the frames selected by the various viewers are multiplexed onto a transmission mediums such as the trunk cable of a cable television system, and transmitted at the standard television frame rate, e.g. 30 frames per second under the NTSC standard, over a channel associated with the video presentation service. Frame stores are positioned at various locations along the length of the transmission medium, and each is provided with a match code, for example an address. When a video frame is labelled with the match code of a particular frame store, that frame store identifies the frame, stores it in a memory, and then continually retransmits the stored frame at the standard television frame rate to the viewer's television receiver. The continually transmitted frame appears as a still frame on the viewer's television receiver. When the next frame in the presentation is required, this frame is retrieved, labelled with the appropriate code, and transmitted to the frame store for display in the same manner. This process is repeated for all the frames in the still-frame presentation.
A sequence of frames may be sent for each still-frame presentation. If still frames are delivered at sufficient rate, the presentation takes on the appearance of reduced motion rather than distinct still frames. For example, if frames are sent at a rate of 6 per second, 5 concurrent user presentations are possible over a single television channel (having 30 frame per second capacity) with reduced motion. Additional processing within the frame store unit can interpolate several images to display additional images, with the object of producing the appearance of smoother motion.
With increasing acceptance of the value of interactive television system services, there is a clear benefit to the industry to provide an efficient transmission medium for these services. The high cost of dedicating a television channel solely to an interactive service is viable only for the largest of such services. Furthermore, it is highly desirable to include interactive capabilities with many of the broadcast services, such as distance learning, being transmitted via satellite, to provide a means for measuring the effectiveness of these services. Combining the transmission of interactive services with these services on one channel would save the cost of an additional channel while providing the benefits of interactive capabilities.
Accordingly, it is an object of the present invention to provide a television system which expands the program capacity of each channel of the television system by distributing at least two distinct presentations concurrently on a single channel. It is a further object of the present invention to address the above-mentioned needs by providing a television system which is capable of distributing multiple viewer requested (interactive) and/or broadcast video presentations, to different respective viewers by means of a single television channel, including the combination of full motion, reduced motion and still-frame video presentations. It is a further object of the present invention to provide a combination of presentations that be dynamically variable so that the system can respond to changing presentation requests over time.